Study Rundown: Improved accuracy and availability of cardiac troponin assays has made this biomarker a key criterion for the diagnosis of myocardial infarction (MI). The specificity of troponin levels for acute MI is limited however, with older patients and those with chronic coronary disease often having elevated levels in the absence of acute coronary syndromes. To differentiate ongoing injury from an acute MI, the percent change in cardiac troponin over 6 hours (delta troponin) has replaced one-time percentile cutoffs for diagnosis. This change is supported by data suggesting improved sensitivity and specificity with delta troponin (see “Relevant Reading”).

The authors of this paper reviewed 1178 cases of NSTEMIs diagnosed independent of delta troponin and found that 26% would be missed if the delta troponin criterion were required. The purpose of introducing delta troponin calculations was to reduce false positives, so some loss of sensitivity is expected. However, the question remains on whether 26% is an acceptable proportion to miss with this test. One possible explanation is that the majority of missed NSTEMIS were old infarctions where myocyte injury had stabilized by the time 6 hour serial measurements were taken. If this is the case, 26% would be less concerning as delta troponin testing is not intended for old infarcts which benefit less from revascularization interventions. Additionally, the lack of a gold standard to define NSTEMI cases complicates the analysis. Given the implications on mortality and variety of presentation in low delta troponin NSTEMI cases shown in this paper, reassessment of the criteria for defining NSTEMI may be warranted.

In-Depth [retrospective analysis]: Among 1178 patients diagnosed with NSTEMI by a cardiologist, 26% had a small relative change of <20% to their cardiac troponin after 6 hour serial measurements. The proportion of patients diagnosed with NSTEMI from the group with <20% change in troponin levels did not differ significantly from the group with a 20-60% change (79% and 83%, p=0.47). Patients diagnosed with NSTEMIs without meeting delta troponin criteria were more likely to present with primary symptoms other than chest pain, have experienced longer symptom duration, and less likely to receive revascularization interventions.

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